Description: This proposal seeks to examine the interrelations of biological, psychological, and social functioning in a cohort of 100 infants from 6 months to 2 years, and a second cross-sectional cohort of 150 subjects at 6, 15, and 24 months of age. The purpose of studying these cohorts is to delineate neuroendocrine measures that are linked to characteristics of infants that may predispose them to mental health problems. The subjects and their caretakers predispose them to mental health problems. The subjects and their caretakers will be assessed using salivary cortisol and a laboratory stress procedure (maternal separation and maternal still face) in an attempt to describe and explain the interaction of caregiver characteristics with infant regulatory features (sleeping, feeding, feeding, and crying) that define a construct of dysregulation. In addition, the study seeks to explore the establishment and predictability of circadian rhythms in children as an antecedent to stable basal cortisol levels indicative of a "less reactive" stress LHPA axis.